A chew toy, such as a dog bone, is commonly made of a thermoplastic material, such as polyethylene, polyurethane, or nylon. Some prior art thermoplastic chew toys are flavored or scented to make the chew toy more attractive to a domestic animal, such as a dog. Such prior art flavored or scented chew toys are made by the processes of: aqueous impregnation with animal by-product; mixing the thermoplastic material with a starch-based flavoring; mixing the thermoplastic material with an oil-based flavoring extract; or mixing the thermoplastic material with animal meal.
Aqueous impregnation with animal by-product typically involves the separate steps of first injection molding the chew toy, and then boiling the chew toy in a broth containing animal parts or animal by-product. Boiling time varies with the thermoplastic material used. For example, the chew toy is boiled for up to 2 hours if the toy is made of polyurethane, and up to 20 hours if the toy is made of nylon.
Aqueous impregnation with animal by-product requires the extra step of boiling the chew toy, which adds time and expense to the manufacturing process. The large boiling tank or pressure cooker required for aqueous impregnation with animal by-product can be an expensive piece of equipment. The tank occupies space in a factory that could be used for other purposes. The cost of energy needed for boiling or pressure cooking raises production costs. Depending on the thermoplastic material used to make the chew toy, the boiling process can take up to 20 hours, which will slow down production. Last, aqueous impregnation using animal by-product results in only small penetrations into the chew toy, on the order of three microns. This small amount of penetration causes the toy to lose its flavor or scent once the surface layer of the toy has been chewed up.
Another prior art chew toy has been made which combines a large amount of corn starch with polyethylene. Polyethylene is a less durable thermoplastic material than polyurethane or nylon, and can be chewed into pieces and splinters by the animal. The animal may swallow the pieces and splinters of polyethylene, which can cause the animal to choke. Polyethylene is not digestible by animals, and can cause complications in an animal's digestive system if it is swallowed. Another problem with this type of chew toy is that it contains a high percentage of starch, which causes the chew toy to grow mold and to have a relatively short shelf life. Additionally, the high percentage of starch makes the chew toy biodegradable, which may cause the toy to disintegrate when moistened (e.g., when chewed).
Flavoring or scenting a chew toy with an oil-based flavor or scent additive typically involves mixing the oil-based additive to a solidified or melted thermoplastic material and injection molding the mixture to form a chew toy. The oil-based additive is typically carried by thermoplastic pellets, which are mixed in with the solid or melted thermoplastic material. The oil extract is typically not compatible with thermoplastic materials, and the resulting chew toy therefore has a surface migrating flavor or scent as the oil extract is constantly urged to the surface of the chew toy.
Surface migration resulting from the use of oil-based additives may cause the flavor or scent to be used up quickly as the animal chews through the surface layer of the toy. Uniform dispersion of flavor or scent throughout the useful life of the toy is made impossible due to the surface migrating characteristic of the oil extract in thermoplastic materials. Another disadvantage is that the oil extract carried by thermoplastic pellets is relatively expensive, which is usually reflected in the increased cost of the chew toy.
Forming a thermoplastic chew toy with animal meal typically involves sifting ground animal meat and by-product to remove pieces that are larger than a selected maximum size, then mixing the meal with thermoplastic beads, melting the beads, and then injection molding the mixture into a selected chew toy shape.
The problem with using animal meal in the chew toy is that grinding and sifting the meal can be a time consuming and difficult task. Meat and animal by-product may be relatively expensive. Also, the particles have to be small enough to be suspended in the toy, therefore, some meat may have to be ground and reground and sifted. Those pieces that cannot be acceptably reduced in size are discarded as waste. Using meat and animal by-products adds saturated fat and cholesterol to the chew toy, which may be detrimental to the animal's health and undesirable to pet owners.
The above methods for adding flavor or scent to a chew toy have inadequacies in cost, time, flavor and scent dispersion, and health effects.